A conventionally known air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building, includes a refrigerant circuit that connects an outdoor unit, which is a heat source unit arranged outside the building, and an indoor unit arranged inside the building to each other by a pipe. In the refrigerant circuit, refrigerant circulates, and the refrigerant transfers or removes heat to heat or cool indoor air, thereby performing heating or cooling of an air-conditioned space.
When a plurality of heat exchangers connected to each other in parallel are used as evaporators like outdoor heat exchangers during a heating operation, the plurality of heat exchangers are connected to each other in parallel through which refrigerant flows. This can reduce pressure loss in the evaporators, improves the performance of the evaporators, and improves the heating performance.
When the plurality of heat exchangers are used as condensers during a cooling operation, however, the plurality of heat exchangers are connected to each other in parallel through which refrigerant flows, resulting in a reduction in the flow speed of the refrigerant flowing through the condensers. This reduces an intra-pipe heat transfer coefficient, reduces the performance of the condensers, and reduces the cooling performance.
To address the above issue, there is a technique for switching flow paths by using a plurality of flow switching valves to improve the performance of both the condensers and the evaporators. In this technique, when a plurality of heat exchangers are used as condensers, flow paths are switched to connect the plurality of heat exchangers to each other in series through which refrigerant flows. This increases the flow speed of the refrigerant, thereby improving the performance of the condensers. When the plurality of heat exchangers are used as evaporators, the flow paths are switched to connect the plurality of heat exchangers to each other in parallel through which refrigerant flows. This reduces pressure loss, improving the performance of the evaporators. Such a technique for improving performance during the cooling operation and the heating operation has been proposed (see, for example, Patent Literatures 1 and 2).